1. Field of Invention
This invention relates to phase modulation of electromagnetic and/or acoustical wavefronts using surface deformation type phase modulators.
2. Description of Prior Art
Prior art concerning surface deformation type phase modulators will be broadly classified into two categories. Those devices using monolithic phase modulating media, and those devices using discrete elements. Examples of monolithic phase modulating include oil films, elastomer layers, piezoelectric media, glass substrates, and thin membranes. Devices employing monolithic media exhibit deformations which are non-localized. This is undesirable since it imposes a limit on spatial resolution.
Discrete element modulators offer a device philosphy amenable to isolation, thereby permitting high spatial resolution. Previous discrete element modulators utilizing piezoelectric shear mode elements include U.S. Pat. No. 3,544,202 to Fowler, Dec. 1, 1970 and U.S. Pat. No. 4,736,132 to Culp, Apr. 5, 1988. In both of these configurations, one electrode functions as a motion constraint by affixing it to a rigid support structure. Separate surfaces are dedicated to the phase modulation and electrode functions. This mounting technique is limited in how it may influence the stress distribution in the piezoelectric element.
In discrete, closely packed arrays, adjacent elements must be electrically isolated. In U.S. Pat. No. 4,736,132, to achieve electrical isolation, a restriction must be placed on the potential that can be applied to adjacent electrodes or at least one additional electrical insulator must be added between adjacent electrodes. Using the latter approach adds fabrication steps and reduces spatial resolution of the array. This is contrary to the philosophy of discrete element arrays. Restricting the potentials applied to adjacent electrodes under utilizes device capability. Furthermore, the support structure of U.S. Pat. No. 4,736,132 provides no assistance in isolating adjacent electrodes.
Shear mode actuators have been utilized in other applications unrelated to phase modulation of electromagnetic wavefronts. Examples include U.S. Pat. No. 4,879,568 to Bartky et al, Nov. 7, 1989.
The shear mode actuators of U.S. Pat. No. 4,879,568 must provide a sealed channel for use as an ink jet droplet generator. As identified in FIGS. 2(a) and 3(a), a compliant strip seal 54 and a continuous compliant strip seal 541 are essential components for this application. As to be identified herein, no such components are required in wavefront phase modulator configurations. Consequently, U.S. Pat. No. 4,879,568 would contain extraneous components if this configuration were contemplated for a new use application involving wavefront phase modulation. Such extraneous components hinder wavefront phase modulator performance. Dual end constraints, necessary for a sealed channel, exist in some form in the remaining embodiments of U.S. Pat. No. 4,879,568.
In addition, no provisions are provided for an optically reflective surface to phase modulate an incident wavefront. As well understood by those knowledgeable in the state of the art, optically reflective surfaces could be metal, but not all metal surfaces are optically reflective surfaces, i.e. gold strongly absorbs in certain "optical" portions of the electromagnetic spectrum. Specifying metal electrodes is not a sufficient condition for producing optically reflective surfaces. Such a specification could severely restrict the spectral flexibility of deformable mirror spatial light modulators. Not specifying an optically reflective surface renders this device dubious for wavefront phase modulator applications.
Furthermore, as well understood by those knowledgeable in the state of the art, no optically reflective surface provisions are identified for the surface most effective for phase modulation in the embodiment illustrated in FIGS. 6(a) or 6(b). Not identifying an optically reflective surface for use in this application renders this embodiment unsuitable for use in wavefront phase modulators. Not maintaining a consistent, suitable set of requirements, suggests that U.S. Pat. No. 4,879,568 was not contemplated for use as an electromagnetic wavefront modulator.
No suitable one or two dimensional wavefront modulator array configurations are available in U.S. Pat. No. 4,879,568. Linear arrays of shear mode actuators are identified in FIG. 9(a). Adjacent shear mode actuators are displaced perpendicular to the surface, when the elements are unenergized, which would be most effective in phase modulation applications. This superimposes all metal electrodes. If a wavefront to be modulated were incident on a metal electrode of an exposed shear mode element, then, due to the nature in which the remaining elements are arranged in FIG. 9(a), the exposed element would eclipse the remaining elements, rendering them useless in phase modulation applications. Two dimensional arrays formed from a plurality of such one dimensional arrays would not be capable of phase modulation in two spatial degrees of freedom. No suitable spatial distribution of shear mode actuators has been identified in U.S. Pat. No. 4,879,568 which could allow shear mode elements to effectively, efficiently, and consistently function as linear or two dimensional wavefront phase modulators involving electromagnetic and/or acoustic wavefronts.
Since U.S. Pat. No. 4,879,568 is plagued by extraneous components, no acceptable and/or an inconsistent definition of optically reflective surfaces and an unsatisfactory spatial distribution of shear mode elements for use in linear and/or two dimensional phase modulators, U.S. Pat. No. 4,879,568 is deemed unacceptable for new use applications involving phase modulation of electromagnetic and/or acoustic wavefronts.
The pitfalls of U.S. Pat. No. 4,879,568 are shared by other ink jet droplet generators.